We have a  problem,  "Screen elements F[xxxxxx] not found" and suspect this may be due to "low speed connection" being activated. Can you confirm?

When the low speed connection is turned on, SAP does not send the technical names to the frontend. So in the GuiXT script you can work with the field labels, e.g. [Business area] or fields positions, but not with the technical names like [BSEG-GSBER].
Our experience is that the low speed connection does not make a significant difference in speed or network load, since the technical names are not a high percentage of the total screen record sent to the frontend.
In the past, when SAP worked with simpler screens and people often used a 9.600 line to connect, this made some difference.